Dowel type fasteners for wood and other type joints are well known. In the past, such dowel fasteners have either been solid and used for alignment purposes in conjunction with adhered or glued joints or have been slotted, solid or tubular dowels which frictionally engage the inside surfaces of bores or apertures in the joint members in which they are inserted. Although certain of the prior known slotted dowels or pins have included spiral or helical slots, the vast majority have included rectilinear slots. Such rectilinearly slotted dowels are less than satisfactory for furniture or other joints because, if inserted in a slot or elongated aperture, it is possible that the slot area of the circumference of such dowel could engage the side of the slot or aperture and produce a loose fit and less than satisfactory frictional holding power.
With certain of the prior spiral or helically slotted dowels, difficulty has been encountered during insertion of such dowels between joint members. Many of such dowels have been stiff and inflexible due in part to the material thickness necessary for their strength.
In other dowel fasteners, tapered ends have been provided as an aid to insertion in the joint members. In many of these, the taper was insufficient to allow proper insertion of the relatively stiff dowel into two holes which might be slightly out of alignment in opposing joint members or sufficiently small to obtain a proper frictional hold in softer materials. Further, such tapered ends have often tended to collapse when struck for insertion of the opposite end in a joint structure thereby eliminating the ability to insert the collapsed end into its respective joint member. Where the taper was sufficiently reduced to avoid such collapse, the aperture or bore size with which the stiff slotted dowel could be used was severely limited. In addition, slotted, dowel type fasteners were often inserted in holes or apertures which were undersized thereby causing over compression and collapse of the dowel diameter or splitting of the joint member. Such collapse or deformation was regulated by controlling the bore size even though the dowel itself had no structure to prevent such insertion.
As in improvement over these prior known problems with slotted dowel fasteners for furniture or other joints, the dowel fastener of U.S. Pat. No. 4,474,493 was introduced. While providing solutions for many of the above problems, such improved dowel fasteners often encountered the problem of nesting during manufacture and use. Nesting comprises the telescoping, overlapping reception of the wall of one tubular type dowel such as that shown in U.S. Pat. No. 4,474,493 through the slot of another similar dowel such that two dowels “nest” together in a substantially overlapping concentric assembly which not only prevents proper coating or heat treatment of the surfaces of the dowel when formed from metal, but also prevents the feeding of individual dowels with automatic feeding machines adapted to automatically install the dowels in joints. Even when such dowels are manually inserted, it was often necessary for the operator/installer to “de-nest” or separate two dowels from one another before insertion in the joint. This caused significantly increased assembly time and increased costs.
During use of the dowel fastener of U.S. Pat. No. 4,474,493, a need was also recognized for increased frictional force for joint retention in certain types of joints. Depending on the type and hardness of the wood or other material from which the joint was formed, tight, secure retention of the joint members was difficult, especially with harder woods or metallic materials thereby indicating a need for increased frictional retention force. With dowel fasteners other than those of U.S. Pat. No. 4,474,493, increasing the frictional retention force was difficult because increasing the size or thickness of the material from which the dowels were made greatly increased the difficulty of insertion of the dowels in the joints, limited the size of joints in which the prior known dowel fasteners could be used, or damaged or split the joints during use.
Therefore, the need was recognized for an improved dowel fastener which could offer increased holding power, avoid nesting problems making use in automatic feeding machines difficult or increasing assembly time due to required de-nesting, provide consistent frictional engagement force, be sufficiently flexible and resilient to allow insertion in varying holes or aperture sizes, allow insertion in slightly non-aligned or non-concentric holes or apertures and yet prevent insertion in holes or apertures, that were undersized and would cause plastic deformation or failure of the dowel.